1. Field of the Invention
The present invention relates to a sub headlight unit and a sub headlight system for use in a vehicle that leans into turns, and a vehicle that leans into turns.
2. Description of the Related Art
In general, in a vehicle that leans into turns (such as saddle-ride type vehicles including motorcycles, three-wheeled motor vehicles, snowmobiles, and ATVs (all terrain vehicles), for example), when the vehicle corners or turns at an intersection, a rider operates a handlebar and additionally shifts his/her own weight in order to counteract centrifugal force acting on a vehicle body. As a result, the vehicle turns with an attitude (hereinafter, also referred to as “lean attitude”) leaning to the inner side of a curve. On the other hand, in a vehicle that does not lean into turns, for example, in an automobile, when the vehicle corners or turns at an intersection, a rider operates a steering wheel and turns with centrifugal force acting on a vehicle body. Therefore, in the vehicle that does not lean into turns, the vehicle body leans to the outer side of a curve due to the centrifugal force.
In the vehicle that leans into turns, the turning is made with an active use of the weight shifting of the rider himself/herself. Therefore, the vehicle body largely leans. In the vehicle that does not lean into turns, the vehicle body leans to the outer side of the curve due to the centrifugal force. The degree of this leaning varies depending on the running speed of the vehicle and the magnitude (radius) of the curve, and this leaning of the vehicle body is not utilized for the turning. In the vehicle that does not lean into turns, it is preferable that the amount of leaning to the outer side of the curve due to the centrifugal force is small.
Thus, at a time of cornering or turning at an intersection, the vehicle that leans into turns causes the vehicle body to lean to the inner side of the curve with a relatively large amount of leaning, while the vehicle that does not lean into turns causes the vehicle body to lean to the outer side of the curve with a relatively small amount of leaning.
Normally, a vehicle is provided with a plurality of lights irrespective of whether or not the vehicle leans into turns. The lights include a light intended mainly to ensure a field of view of a rider of the vehicle and a light intended mainly to allow a surrounding vehicle or the like to recognize the presence of the rider's own vehicle. A headlight is the light intended mainly to ensure the field of view of the rider of the vehicle, and in general, is configured to switch between a high beam (running headlight) and a low beam (passing headlight).
The high beam, which emits light in a horizontal (upward) direction, ensures a field of view at a long distance. Generally, in order to avoid blinding or impairing the vision of a rider of a nearby or oncoming vehicle, the high beam is used in a situation where there is no vehicle or the like existing ahead at night. The low beam, which emits light in a downward direction, is used even in a situation where there is a vehicle or the like existing ahead. Therefore, in a normal case, a vehicle often runs with the low beam turned on.
When the vehicle that leans into turns is running on a straight road, an illumination range of a headlight light source (low beam) spreads evenly to the left and right in an area ahead in an advancing direction and below a horizontal plane including the headlight light source. When the vehicle that leans into turns is running on a road curving to the left, the vehicle runs with the vehicle body inclined to the left. Accordingly, the illumination range of the headlight light source spreads downward to the left. As a result, a nearer position on a running lane is illuminated. Thus, the illumination range in an area inside the curve and ahead in the advancing direction is reduced.
Therefore, a vehicle has been proposed in which, in addition to a main headlight that illuminates an area ahead of the vehicle, a pair of right and left sub headlights that are turned on depending on the magnitude of a lean angle (angle of inclination of a vehicle body to the inner side of a curve relative to an upright state thereof) are provided as the headlight (Japanese Patent No. 4806550). A vehicle has been also proposed in which a mirror placed at the upper side of a headlight light source is rotated in accordance with the magnitude of a lean angle so that an optical axis of the headlight light source is changed. See, for example, the article entitled, “BMW Motorrad adaptiver Scheinwerfer” [online], uploaded on Jul. 2, 2010 [retrieved on Mar. 12, 2012], from Internet (URL: http://www.youtube.com/watch?v=ErPRzhFxJpc), hereinafter referred to as “the BMW article”.
A situation under which the vehicle corners or turns at an intersection is not always the same. A rider's field of view at a time of turning a curve varies depending on the vehicle speed and also on the radius of a road, and the like.
For example, even on a road having a curve with the same radius, some vehicles move through the curve at a relatively low speed, and other vehicles move through the curve at a relatively high speed. At this time, the lean angle of the vehicle moving at the high speed is larger than the lean angle of the vehicle moving at the low speed. Accordingly, an illumination range of a headlight of the vehicle moving at the high speed decreases as compared with an illumination range of a headlight of the vehicle moving at the low speed. Therefore, a visible range ahead in a path varies depending on the vehicle speed.
Furthermore, even when the vehicle is running at the same speed, the lean angle is small in a curve with a large radius so that the illumination range is reduced to a small extent, while the lean angle is large in a curve with a small radius so that the illumination range is reduced to a large extent. Accordingly, for example, in a case of continuously moving through a plurality of curves having different radii during touring on a mountain road, the illumination range of the headlight changes in each curve even though the speed does not change so much. As a result, the field of view ahead in a path changes. When such a change in the field of view ahead in a path during a curve is small, a rider is more likely to feel safe.
In the vehicle disclosed in Japanese Patent No. 4806550, the pair of right and left sub headlights are turned on in accordance with the lean angle. Here, in order to prevent blinding or impairing the vision of a rider of a nearby or oncoming vehicle, or the like, it is preferable that, at a time of running on a curve, a light emission direction of the sub headlight is lower than a horizontal plane. Under such restricted circumstances, a problem arises that it is difficult to sufficiently suppress, by means of a pair of right and left sub headlights, a change in the field of view ahead in a path caused by a difference in a situation of moving through a curve.
On the other hand, in the headlight unit of variable optical axis type disclosed in the BMW article, the mirror is rotated in accordance with the magnitude of the lean angle, and thereby the orientation of the optical axis can be continuously changed. Thus, even under the restriction that the light emission direction of the headlight should be lower than the horizontal plane, it is easy to suppress a change in the field of view ahead in a path. Moreover, a change in the optical axis direction of the headlight itself is used to respond to a reduction in the illumination range of the headlight. This achieves a compact size of the headlight unit. Thus, the headlight of variable optical axis type disclosed in the BMW article has a compact size, and is quite useful.
However, as a result of testing, in a wide variety of running scenes, a vehicle including the headlight unit of movable optical axis type disclosed in the BMW article, the following was revealed. That is, in some scenes, it is desirable to illuminate a position still farther from the vehicle on a path. In order to largely change the light emission direction for such a scene, for example, it is necessary to increase the size of a movable member such as the mirror, or to provide another movable member, or to increase the size of a reflector and a bracket in order to ensure a wide movable range of the mirror. This causes a problem that the size of the headlight unit increases, which is not suitable for a vehicle that leans into turns.